CPM, or cost per thousand impressions, is a form of measurement used by online publishers and ad serving programs to determine advertiser costs. Usually based on a fixed amount agreed upon by the advertiser, costs can also be based on competitive bidding at the keyword level.
For example, an affiliate marketing program may allow the advertiser to select a maximum bid amount for each keyword that is in his campaign. An impression of the advertiser’s content generated by a specific keyword within a particularly high competitive bidding environment may result in a higher CPM amount for all impressions that occur at that time.
Be sure to read through the rules of the ad serving or affiliate marketing program so you understand exactly how the cost structure works.
See also Impressions, Affiliate Marketing, Search Engine Marketing, CPC-Cost per Click, CTR-Click Through Rate, PPC-Pay per Click, Online Advertising, Internet Advertising, Conversion Rate